Power correction module for power amplifiers

ABSTRACT

A power correction module for use with an amplifier driving a load impedance is configured to sample the supply current and to cause a change in a control voltage, which corrects the supply voltage in response to a change in the load impedance. The supply voltage is corrected to cause the power amplifier to have a substantially constant output power. The power correction module is further configured to output a corrected peak voltage determined by an average value of the supply current.

This is a divisional of U.S. patent application Ser. No. 11/895,725,filed Aug. 27, 2007, now U.S. Pat. No. 7,937,049 entitled “Output PowerCorrection Module for Amplifiers in Transmitters,” and the benefit ofand priority to that application and a provisional patent applicationentitled “Power Correction Module for Power Amplifiers,” Ser. No.60/850,324, filed on Oct. 6, 2006, is hereby claimed, and thedisclosures of which are hereby incorporated fully by reference into thepresent application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of electrical circuits. Moreparticularly, the invention relates to amplifier circuits.

2. Background Art

Power amplifiers, such as saturated power amplifiers, used incommunications devices, such as mobile telephones, are required tooperate under wide variations in load impedance. Under these variationsin load impedance, it is highly desirable for power amplifiers, such assaturated power amplifiers, to maintain a constant output power. It isalso highly desirable for power amplifiers in transmitter systemsutilizing predistortion for complex data modulations, such as datamodulations utilized in the Enhanced Data Rates for GSM Evolution (EDGE)communications standard, to maintain a constant output power under loadimpedance variations. As a result, various techniques have been employedin an attempt to control the output power of a power amplifier.

However, conventional techniques for controlling the output power of apower amplifier suffer various disadvantages. For example, techniquesthat indirectly control the output power by controlling the voltage orcurrent, such as collector voltage or collector current, supplied to thepower amplifier provide adequate compensation for variations inoperating conditions, such as variations in temperature and supplyvoltage, but undesirably allow significant variations in power deliveredto a varying load. For example, in the voltage or current controltechniques discussed above, the power delivered to the load by the poweramplifier can vary by as much as 10.0 decibels (dB) as the impedance ofthe load changes.

In another conventional approach, a constant DC power is delivered to apower amplifier, such as a saturated power amplifier, by utilizing afeedback loop to adjust the collector voltage of the power amplifier.Since the power amplifier output power is equal to the product of the DCpower and the collector efficiency, this approach can provide a constantoutput power if constant collector efficiency is maintained. However,this approach presents significant problems in transmitter systemsutilizing predistortion, such as transmitter systems utilizing polarEDGE modulation.

SUMMARY OF THE INVENTION

An output power correction module for amplifiers in transmitters,substantially as shown in and/or described in connection with at leastone of the figures, as set forth more completely in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary conventional transmittersystem.

FIG. 2 is a block diagram of an exemplary transmitter system includingan exemplary power correction module in accordance with one embodimentof the present invention.

FIG. 3 is a block diagram of an exemplary power correction module inaccordance with one embodiment of the present invention.

FIG. 4 illustrates a circuit diagram of an exemplary powercontrol/current detection circuit in accordance with one embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to an output power correction modulefor amplifiers in transmitters. The following description containsspecific information pertaining to the implementation of the presentinvention. One skilled in the art will recognize that the presentinvention may be implemented in a manner different from thatspecifically discussed in the present application. Moreover, some of thespecific details of the invention are not discussed in order not toobscure the invention. The specific details not described in the presentapplication are within the knowledge of a person of ordinary skill inthe art.

The drawings in the present application and their accompanying detaileddescription are directed to merely exemplary embodiments of theinvention. To maintain brevity, other embodiments of the invention whichuse the principles of the present invention are not specificallydescribed in the present application and are not specificallyillustrated by the present drawings.

The present invention provides an innovative power correction module forcorrecting output power of a power amplifier in a transmitter systemunder variations in load impedance. Although a transmitter systemutilizing polar modulation, such as polar EDGE modulation—which requirespredistortion and provides both phase and amplitude modulation—isutilized to illustrate the present invention, the present invention canalso be applied in a transmitter system in which amplitude modulation orpredistortion are not utilized.

FIG. 1 shows a block diagram of an exemplary conventional transmittersystem coupled to a load. Certain details and features have been leftout of FIG. 1, which are apparent to a person of ordinary skill in theart. Conventional transmitter system 100, which is coupled to load 103,includes baseband module 102, phase modulator 104, power amplifier 106,and power control circuit 108. Baseband module 102 includes coordinateconverter block 110, peak voltage computation block 112, multiplicationelement 114, and predistortion module 116, which includes controlvoltage (V_(CNTL)) look-up table 118, phase shift (ΔΦ) look-up table120, and summation element 122. Conventional transmitter system 100 canbe utilized in a wireless communications device, such as a mobiletelephone, that can utilize a communications standard, such as an EDGEcommunications standard. Conventional transmitter system 100 can alsoutilize polar modulation, such as polar EDGE modulation, which utilizespredistortion.

As shown in FIG. 1, desired average output power (P_(desired)) 124,which is a desired average output power of power amplifier 106, iscoupled to the input of peak voltage computation block 112 and theoutput of peak voltage computation block 112 is coupled to an input ofmultiplication element 114. Peak voltage computation block 112 can beconfigured to receive P_(desired) 124, compute a corresponding averagepeak voltage (V_(PK(avg))) corresponding to P_(desired) 124, and outputV_(PK(avg)) (indicated by arrow 126) to multiplication element 114. Alsoshown in FIG. 1, I/Q signal 128, which can be utilized to provideamplitude and phase modulation information, is coupled to the input ofcoordinate converter block 110 and the respective outputs of coordinateconverter block 110 are coupled to inputs of multiplication element 114and summation element 122. Coordinate converter block 110 can beconfigured to receive I/Q signal 128, convert I/Q signal 128 fromCartesian coordinates (I, Q) to polar coordinates (ρ, Φ), where “ρ” isan ideal amplitude modulation component and “Φ” is an ideal phasemodulation component, to filter the resulting signal, and to output ρ(indicated by arrow 130) and Φ (indicated by arrow 132) to respectiveinputs of multiplication element 114 and summation element 122. Theconversion from Cartesian coordinates (I, Q) to polar coordinates (ρ, Φ)can be performed by, for example, a baseband processor, which is notshown in FIG. 1.

Further shown in FIG. 1, the output of multiplication element 114 iscoupled to the input of V_(CNTL) look-up table 118 and the output ofV_(CNTL) look-up table 118 is coupled to the inputs of ΔΦ look-up table120 and power control circuit 108. Multiplication element 114 can beconfigured to receive V_(PK(avg)) and ρ, form the product of ρ andV_(PK(avg)) (ρ●V_(PK(avg))), and to output ρ●V_(PK(avg)) to V_(CNTL)look-up table 118. V_(CNTL) look-up table 118 can be configured toreceive the product of ρ●V_(PK(avg)) and to determine a correspondingpredistorted control voltage (V_(CNTL)), and to output V_(CNTL)(indicated by arrow 132) to ΔΦ look-up table 120 and power controlcircuit 108. Also shown in FIG. 1, the output of ΔΦ look-up table 120 iscoupled to an input of summation element 122 and the output of summationelement 122 is coupled to an input of phase modulator 104. ΔΦ look-uptable 120 can be configured to receive V_(CNTL) from V_(CNTL), look-uptable 118, utilize V_(CNTL), to determine an appropriate amount of phaseshift (ΔΦ) corresponding to V_(CNTL) to apply to the ideal phasemodulation component, i.e., Φ, and to output ΔΦ (indicated by arrow 134)to an input of summation element 122. V_(CNTL), look-up table 118 and ΔΦlook-up table 120 can be formed during a calibration procedure for acommunications device, such as a mobile telephone, in which transmittersystem 100 resides.

Summation element 122 can be configured to form the sum of ΔΦ and Φ toform a predistorted phase modulation component (Φ′), and to output Φ′(indicated by arrow 136) to an input of phase modulator 104. Furthershown in FIG. 1, RF carrier 138 is coupled to an input of phasemodulator 104 and the output of phase modulator 104 is coupled to thesignal input of power amplifier 106. Phase modulator 104 can be a polarmodulator, such as an EDGE polar modulator, and can be configured tomodulate RF carrier 138 with Φ′ and to output a phase modulated RFsignal, i.e., RF IN 140, which is coupled to the signal input of poweramplifier 106. Also shown in FIG. 1, the output of power control circuit108 is coupled to a supply voltage input, i.e., a collector voltageinput, of power amplifier 106 and load 103 is coupled between the outputof power amplifier 106 and ground 142. Power control circuit 108 can beconfigured to receive V_(CNTL), i.e., a predistorted control voltage,from V_(CNTL) look-up table 118 in predistortion module 116 and toprovide a collector current (I_(CC)) (indicated by arrow 144) and acollector voltage (V_(CC)) (indicated by arrow 146), to power amplifier106. Power control circuit 108 can include a linear regulator (not shownin FIG. 1) such that V_(CC) is linearly related to V_(CNTL).

Power amplifier 106 can be a saturated power amplifier and can beconfigured to receive RF IN 140, which is a phase-modulated RF signalprovided by phase modulator 104, to combine the predistorted phase andamplitude modulation components at the collector of power amplifier 106,and to output an RF signal, i.e., RF OUT 148, having accurate phase andamplitude modulation. Load 103, which can be, for example, an antenna,can provide a load impedance between the output of power amplifier 106and ground 142. The load impedance provided by load 103 can be designedto be, for example, 50.0 ohms. However, under adverse voltage standingwave ratio (VSWR) conditions, the load impedance presented to poweramplifier 106 by load 103 can vary significantly from an ideal designedload impedance, such as a 50.0 ohm load impedance.

When the load impedance presented to power amplifier 106 varies, theoutput power provided by power amplifier 106 also varies. However,V_(CNTL), which determines V_(CC), is not corrected for a change in theload impedance. Thus, conventional transmitter system 100 does notprovide correction for variations in load impedance. Therefore, theoutput power provided by power amplifier 106 in conventional transmittersystem 100 can vary during variations in the load impedance of load 103.

FIG. 2 shows a block diagram of an exemplary transmitter system coupledto a load in accordance with one embodiment of the present invention.Certain details and features have been left out of FIG. 2, which areapparent to a person of ordinary skill in the art. Transmitter system200, which is coupled to load 203, includes baseband module 202, phasemodulator 204, power amplifier 206, and power control/current detectioncircuit 208. Baseband module 202 includes coordinate converter block210, peak voltage computation block 212, multiplication element 214,power correction module 224, and predistortion module 216, whichincludes control voltage (V_(CNTL)) look-up table 218, phase shift (ΔΦ)look-up table 220, and summation element 222. Transmitter system 200 canbe utilized in communications devices, such as mobile telephones, thatutilize an EDGE communications standard or other suitable communicationsstandards. Transmitter system 200 can utilize, for example, open-looppolar EDGE modulation, which utilizes predistortion. However,transmitter system 200 can also utilize other types of polar modulation.

As shown in FIG. 2, desired average output power (P_(desired)) 226,which is a desired output power of power amplifier 206, is coupled tothe input of peak voltage computation block 212 and the output of peakvoltage computation block 212 is coupled to an input of power controlmodule 224. Peak voltage computation block 212 can be configured toreceive P_(desired) 226, to compute an average peak voltage(V_(PK(avg))) corresponding to P_(desired) 226, and to outputV_(PK(avg)) (indicated by arrow 228) to an input of power correctionmodule 224. Also shown in FIG. 2, an output of power control/currentdetection circuit 208 is coupled to an input of power correction module224 and the output of power correction module 224 is coupled to an inputof multiplication element 214. Power correction module 224 can beconfigured to receive V_(PK(avg)) from peak voltage computation block212 and V_(ICC) (indicated by arrow 230) from power control/currentdetection circuit 208, to determine a corrected average peak voltage(V_(PK(avg, corrected))) by adjusting V_(PK(avg)) by a correction factor(k), and to output V_(PK(avg, corrected)) (indicated by arrow 232).

The correction factor, i.e., k, can be determined from the equation:

$\begin{matrix}{k = \sqrt{\frac{I_{{CC}{({ideal})}}}{I_{{CC}{({measured})}}}}} & {{equation}\mspace{14mu}(1)}\end{matrix}$where “I_(CC(ideal))” is the ideal collector current that poweramplifier 206 should draw from power control/current detection circuit208 for a desired average peak voltage, i.e., V_(PK(avg)), correspondingto the desired output power, i.e., P_(desired) 226, of power amplifier206, and where “I_(CC(measured))” is a measured average value of thecollector current, i.e., I_(CC) (indicated by arrow 234), drawn by poweramplifier 206. I_(CC(measured)) can be determined from V_(ICC), which isa feedback voltage that is substantially proportional to I_(CC), i.e.,the actual collector current drawn by amplifier 206. Thus, by receivingV_(ICC), power correction module is sampling I_(CC). An embodiment ofthe invention's power correction module is further discussed below inrelation to FIG. 3.

Further shown in FIG. 2, I/Q signal 236 is coupled to the input ofcoordinate converter block 210 and the respective outputs of coordinateconverter block 210 are coupled to multiplication element 214 andsummation element 222. I/Q signal 236 can be utilized to provide phaseand amplitude modulation information. Coordinate converter block 210 canbe configured to receive I/Q signal 236, convert I/Q signal 236 fromCartesian coordinates (I, Q) to polar coordinates (ρ, Φ), where “ρ” isan ideal amplitude modulation component and “Φ” is an ideal phasemodulation component, to filter the signal, and to provide ρ (indicatedby arrow 238) at one output and to output Φ (indicated by arrow 240) atthe other output. The conversion from Cartesian coordinates (I, Q) topolar coordinates (ρ, Φ) can be performed by, for example, a basebandprocessor (not shown in FIG. 2) in baseband module 202.

Further shown in FIG. 2, the output of multiplication element 214 iscoupled to the input of V_(CNTL) look-up table 218 and the output ofV_(CNTL), look-up table 218 is coupled to the inputs of ΔΦ look-up table220 and power control/current detection module 208. Multiplicationelement 214 can be configured to receive V_(PK (avg, corrected)) frompower correction module 224 and ρ from coordinate converter block 210,to form the product of ρ and V_(PK (avg, corrected))(ρ●V_(PK (avg, corrected))), and to output ρ●V_(PK (avg, corrected)) tothe input of V_(CNTL) look-up table 218. V_(CNTL) look-up table 218 canbe configured to receive ρ ●V_(PK (avg, corrected)) from multiplicationelement 214, to determine a control voltage (V_(CNTL)) corresponding toρ ●V_(PK (avg, corrected)) by utilizing an appropriate look-up table,and to output V_(CNTL) (indicated by arrow 242) to the inputs of ΔΦlook-up table 220 and power control/current detection circuit 208.

Also shown in FIG. 2, the output of ΔΦ look-up table 220 is coupled toan input of summation element 222 and the output of summation element222 is coupled to an input of phase modulator 204. ΔΦ look-up table 220can be configured to receive V_(CNTL) from V_(CNTL) look-up table 218,to determine an amount of phase shift (ΔΦ) to add to Φ, i.e., the idealphase component, corresponding to V_(CNTL) by utilizing an appropriatelook-up table, and to output ΔΦ (indicated by arrow 244) to an input ofsummation element 222. The look-up tables in V_(CNTL) look-up table 218and ΔΦ look-up table 220 can be formed during a calibration procedurefor a communications device, such as a mobile telephone, in whichtransmitter system 200 resides. Summation element 222 can be configuredto receive Φ from coordinate converter block 210 and ΔΦ from ΔΦ look-uptable 220, to add Φ and ΔΦ to form Φ′, i.e., a predistorted phasemodulation component, and to output Φ′ (indicated by arrow 246) to aninput of phase modulator 204.

Also shown in FIG. 2, RF carrier 248 is coupled to an input of phasemodulator 204 and the output of phase modulator 204 is coupled to thesignal input of power amplifier 206. Phase modulator 204 can be, forexample, a polar modulator, such as an EDGE polar modulator, and can beconfigured to receive Φ′ from summation element 222 and RF carrier 248,to phase modulate RF carrier 248 with Φ′, and to output a phasemodulated RF signal (RF IN 250) to the signal input of power amplifier206. Further shown in FIG. 2, the output of power control/currentdetection circuit 208 is coupled to a supply voltage input, i.e., acollector voltage input, of power amplifier 206 and load 203 is coupledbetween the output of power amplifier 206 and ground 252.

Power control/current detection circuit 208 can be configured to receiveV_(CNTL), which is a predistorted control voltage, from V_(CNTL) look-uptable 218, to provide a supply voltage (V_(CC)) (indicated by arrow 254)and a supply current (I_(CC)) (indicated by arrow 234) to poweramplifier 206, and to provide V_(ICC) (indicated by arrow 230) to powercorrection module 224. In power control/current detection circuit 208,V_(ICC) is proportional to I_(CC) and V_(CC) is linearly proportional toV_(CNTL). An exemplary power control/current detection circuit isfurther discussed below in relation to FIG. 4.

Power amplifier 206 can be a saturated power amplifier and can beconfigured to receive RF IN 250, which is a phase-modulated RF signal,from phase modulator 204, and V_(CC), which is a predistorted amplitudemodulated supply voltage, from power control/current detection circuit208, to combine the predistorted phase and amplitude components at thecollector of the power amplifier, and to output an RF signal, i.e., RFOUT 256, having accurate phase and amplitude modulation. Load 203, whichcan be, for example, an antenna, has a load impedance, which is providedbetween the output of power amplifier 206 and ground 252. The loadimpedance of load 203 can be designed to be, for example, approximatelyequal to 50.0 ohms. However, the load impedance of load 203 can also bedesigned to be different than 50.0 ohms.

The operation of transmitter system 200 will now be discussed. Underadverse VSWR conditions, the load impedance presented to power amplifier206 by load 203 can significantly vary from a designed “ideal” loadimpedance, which can be, for example, approximately 50.0 ohms. As theload impedance changes, I_(CC) i.e., the supply current drawn by poweramplifier 206, will also change. In the present embodiment, V_(ICC),which is proportional to I_(CC), is provided by power control/currentdetection circuit 208 and coupled to power correction module 224 toprovide a sample of I_(CC). In power correction module 224, V_(ICC) canbe integrated over a predetermined time period to determine anintegrated value of V_(ICC), which can be utilized to determine anaverage value of I_(CC), i.e. I_(CC(measured)). By utilizing a knownideal collector current for the desired average peak voltage, i.e.,V_(PK(avg)), a correction factor (k) can be determined and utilized toadjust V_(PK(avg)) for the load impedance of load 203.

The corrected average peak voltage, i.e., V_(PK(avg, corrected)) can beoutput by power correction module 224, combined with the amplitudemodulation component, i.e., ρ, and input into V_(CNTL) look-up table218. V_(CNTL) look-up table 218 provides a corresponding controlvoltage, i.e., V_(CNTL), which is predistorted to correct fornonlinearities between V_(CC) and the RF output voltage and is inputinto power control/current detection circuit 208. V_(CNTL), which isamplitude modulated and corrected for load impedance, is utilized todetermine V_(CC), which is applied to power amplifier 206. V_(CNTL), isalso input into ΔΦ look-up table 220 to determine an appropriate amountof phase (ΔΦ) to add to the ideal phase modulation component Φ tocorrect for excess phase that can be introduced by modulating thecollector voltage. After the phase is predistorted, it is modulated ontoRF carrier 248 in phase modulator 204 to form RF IN 250, which isapplied to the signal input of power amplifier 206. The predistortedphase and amplitude modulation components are combined at the collectorof power amplifier 206 is produce RF OUT 256, which is a linear outputsignal having accurate phase and amplitude modulation.

By correcting V_(CNTL) for variations in load impedance, V_(CC), whichis determined by V_(CNTL) is also corrected for load impedancevariations. DC power (P_(DC)) is substantially equal to V_(CC)●I_(CC)and output power (P_(RF)) is substantially equal to P_(DC)●η, which isthe collector efficiency of power amplifier 206. By providingsubstantially constant collector efficiency under variations in loadimpedance, the present invention can provide a substantially constantpower amplifier output power under a varying load impedance.

Thus, by utilizing a feedback loop including power control/currentdetection circuit 208, power correction module 224, multiplicationelement 214, and predistortion module 216 and by providing asubstantially constant collector efficiency, an embodiment of thepresent invention can provide output power correction for variations inload impedance at the output of power amplifier 206 so as to provide asubstantially constant power output. In contrast, conventionaltransmitter system 100 does not provide output power correction forchanges in load impedance. As a result, the output power provided bypower amplifier 106 in conventional transmitter system 100 canundesirably vary under variations in load impedance.

Also, since load impedance variations typically occur very slowlycompared to the modulation bandwidth of transmitter system 200, thefeedback control loop provided by the present invention for correctingoutput power for variations in load impedance can be a relatively slowcontrol loop. As a result, polar modulation in transmitter system 200can operate in an essentially open-loop condition. Thus, the presentinvention eliminates the need for high-speed circuitry in the feedbackloop, thereby reducing manufacturing cost.

Additionally, since the present invention provides the baseband module,e.g., baseband module 202, with collector current information,over-current protection can be implemented in software, if desired.

FIG. 3 shows a block diagram of an exemplary power correction module inaccordance with one embodiment of the present invention. In FIG. 3,power correction module 324 corresponds to power correction module 224in transmitter system 200 in FIG. 2. Also, V_(PK(avg)) 328, V_(ICC) 330,and V_(PK(avg, corrected)) 332 in FIG. 3 correspond, respectively, toV_(PK(avg)) (indicated by arrow 228), V_(ICC) (indicated by arrow 230),and V_(PK(avg, corrected)) (indicated by arrow 232) in FIG. 2. Powercorrection module 324 includes multiplication element 338, V_(PK(avg))Correction Factor Block 340 (hereinafter referred to simply as“correction factor block 340”), I_(CC(ideal)) Look-Up Table 342, andintegrator 344. Power correction module 324 can be configured to receiveV_(PK(avg)) 328, which is an average peak voltage that is desired at theoutput of power amplifier 206 in FIG. 2, and V_(ICC) 330, which is afeedback voltage that is proportional to I_(CC), to determine k, whichis a correction factor for adjusting the average peak voltage inresponse to a change in load impedance of load 203, and to outputV_(PK(avg, corrected)) 332, which is a corrected average peak voltage.

As shown in FIG. 3, V_(ICC) 330 is coupled to the input of integrator344 and the output of integrator 344 is coupled to an input ofcorrection factor block 340. Integrator 344 can be configured to receiveV_(ICC) 330, which is a feedback voltage from power control/currentdetection circuit 208 that corresponds to a sample of the supply current(I_(CC)) drawn by power amplifier 206, integrate V_(ICC) 330 over aselected time period, to determine an average value of I_(CC), i.e.,I_(CC(measured)), from the integrated value of V_(ICC) 330, and tooutput I_(CC(measured)) (indicated by arrow 350). Also shown in FIG. 3,V_(PK(avg)) 328 is coupled to the input of I_(CC(ideal)) Look-Up Table342, the output of I_(CC(ideal)) Look-Up Table 342 is coupled to aninput of correction factor block 340, and the output of correctionfactor block 340 is coupled to an input of multiplication element 338.

I_(CC(ideal)) Look-Up Table 342 can be configured to receive V_(PK(avg))328, to determine an ideal collector current, i.e., a collector currentthat would be drawn by power amplifier 206 under a specified loadimpedance, such as a 50.0 ohm load impedance, corresponding toV_(PK(avg)) 328, and to output I_(CC(ideal)) (indicated by arrow 348).I_(CC(ideal)) can be determined from a look-up table that can begenerated during a calibration procedure for a communications device,such as a mobile telephone, in which transmitter system 200 resides.Correction factor block 340 can be configured to receiveI_(CC(measured)) and I_(CC(ideal)), to determine k, a correction factor,from equation (1) discussed above, and to output k (indicated by arrow346) to multiplication element 338.

Further shown in FIG. 3, V_(PK(avg)) 328 is coupled to an input ofmultiplication element 338 and V_(PK(avg, corrected)) 332 is output bymultiplication element 338. Multiplication element 338 can be configuredto receive V_(PK(avg)) 328 and k, to determine the product of k andV_(PK(avg)) 328, and to output a corrected average peak voltage, i.e.,V_(PK(avg, corrected)) 332.

FIG. 4 shows a circuit diagram of an exemplary power control/currentdetection circuit coupled to an exemplary power amplifier in accordancewith one embodiment of the present invention. In FIG. 4, power amplifier406, power control/current detection circuit 408, V_(ICC) 430, I_(CC)(indicated by arrow 434), V_(CNTL) 442, RF IN 450, V_(CC) (indicated byarrow 454) and RF OUT 456 correspond, respectively, to power amplifier206, power control/current detection circuit 208, V_(ICC) (indicated byarrow 230), I_(CC) (indicated by arrow 234), V_(CNTL) (indicated byarrow 242), RF IN 250, V_(CC) (indicated by arrow 254) and RF OUT 256 inFIG. 2. Power control/current detection circuit 408 includes operationalamplifiers (op amp) 460, 462, and 464, feedback network 466, transistors468, 470, and 472, and resistor 478. Transistors 468 and 470 can eachbe, for example, a p-channel field-effect transistor (PFET). Transistor472 can be, for example, an n-channel FET (NFET).

As shown in FIG. 4, power control/current detection circuit 408 iscoupled to power amplifier 406 by inductor 490, which can be, forexample, an RF choke. Inductor 490 can prevent an RF signal in poweramplifier 406 from entering power control/current detection circuit 408.Also shown in FIG. 4, V_(CNTL) 442 is coupled to the negative terminalof op amp 460, feedback network 466 is coupled between the positiveterminal of op amp 460 and the drain of transistor 468, the negativeterminal of op amp 462 and a first terminal of inductor 490 at node 484,and a second terminal of inductor 490 is coupled to a supply voltageinput of power amplifier 406. Node 484 has a voltage referred to hereinas “V_(CC)” (indicated by arrow 454). Feedback network 466 can determinethe gain of the linear regulator formed by op amp 460, feedback network466, and transistor 468 and can be, for example, a resistive feedbacknetwork.

Also shown in FIG. 4, the output of op amp 460 is coupled to the gatesof transistors 468 and 470 and the sources of transistors 468 and 470are coupled to power source 480, which can be a DC power source, such asa battery. Further shown in FIG. 4, the positive terminal of op amp 462is coupled to the drains of transistors 470 and 472, the output of opamp 462 is coupled to the gate of transistor 472, and the source oftransistor 472 is coupled to the positive terminal of op amp 464 and afirst terminal of resistor 478 at node 482. Also shown in FIG. 4, thesecond terminal of resistor 478 is coupled to ground 488 and thenegative terminal of op amp 464 is coupled to the output of op amp 464at node 492, which provides V_(ICC) 430.

The function and operation of power control/current detection circuit408 will now be discussed. Op amp 460, feedback network 466 andtransistor 468 form a linear regulator that receives V_(CNTL) 442 andprovides a supply voltage, i.e., V_(CC), for power amplifier 406 at node484. Power amplifier 406 draws I_(CC) (indicated by arrow 434), which isa supply current provided by power control/current detection circuit408. I_(CC), which is drawn from power source 480, is a large currentthat flows through transistor 468. The product of V_(CC) and I_(CC)determines the DC power provided to power amplifier 406. The currentmirror formed by transistors 468 and 470, which are driven by op amp460, provides a sense current (I_(SENSE)) (indicated by arrow 486),which flows through transistors 470 and 472. I_(SENSE) is substantiallyequal to I_(CC)/N, where “N” is a mirror ratio and is determined by thesize of transistor 468 with respect to the size of transistor 470.

Op amp 462 is utilized to cause the voltage drop across transistor 470to be substantially equal to the voltage drop across transistor 468. Inop amp 462, the voltage at the positive terminal, which is coupled tothe drains of transistors 470 and 472, is constrained to besubstantially equal to the voltage, i.e., V_(CC), at the negativeterminal of the op amp. Thus, op amp 462 forms a feedback loop toincrease the accuracy of the current mirror formed by transistors 468and 470. I_(SENSE) flows through resistor 478 to ground 488, therebycausing V_(ICC) to be formed at node 482. As a result of the currentmirror formed by transistors 468 and 470, V_(ICC) is proportional toI_(CC), i.e., the collector current drawn by power amplifier 406. Op amp464 is configured to operate as a unity gain buffer to provide a highimpedance load on node 482 so as to prevent current from being drawnfrom node 482 and, thereby, altering the relationship between V_(ICC)and I_(CC). The negative terminal of op amp 464 is coupled to the outputof op amp 464, thereby providing V_(ICC) 430 at node 492.

A change in a load impedance of a load, such as load 203 in FIG. 2,coupled to the output of power amplifier 406 can cause a correspondingchange in I_(CC), which is the supply current drawn by power amplifier406. A change in I_(CC) can cause a corresponding change in V_(ICC) 430,which is proportional to I_(CC). In the present embodiment, V_(ICC) 430forms a feedback voltage that can be utilized to sample I_(CC). Byutilizing a feedback loop including power correction module 224,multiplication element 214, and predistortion module 216 in basebandmodule 202 in FIG. 2, V_(CNTL) 442 can be adjusted to compensate for thechange in I_(CC) caused by a change in load impedance. Since V_(CNTL)442 determines V_(CC), the present invention can cause an appropriatechange in V_(CC) so as to advantageously provide a substantiallyconstant power at the output of power amplifier 406 under load impedancevariations.

Thus, by utilizing a power correction module in a feedback loop tosample collector current drawn by a power amplifier, the presentinvention provides power amplifier output power correction undervariations in load impedance. As a result, the present invention canadvantageously provide a substantially constant power amplifier outputpower under load impedance variations. Additionally, the presentinvention can provide a substantially constant output power whileadvantageously performing predistortion, which is required intransmitter systems using a modulation such as open-loop polar EDGEmodulation.

From the above description of the invention it is manifest that varioustechniques can be used for implementing the concepts of the presentinvention without departing from its scope. Moreover, while theinvention has been described with specific reference to certainembodiments, a person of ordinary skill in the art would appreciate thatchanges can be made in form and detail without departing from the spiritand the scope of the invention. Thus, the described embodiments are tobe considered in all respects as illustrative and not restrictive. Itshould also be understood that the invention is not limited to theparticular embodiments described herein but is capable of manyrearrangements, modifications, and substitutions without departing fromthe scope of the invention.

Thus, an output power correction module for amplifiers in transmittershas been described.

1. A power correction module for use with an amplifier driving a load impedance, said power correction module comprising: an integrator configured to generate an average value of a supply current of said amplifier in response to changes in said load impedance; look-up table configured to receive a peak voltage and to determine an ideal value of said supply current; and a correction factor block configured to receive said average value of said supply current and to provide a correction factor, said correction factor being utilized to correct a supply voltage of said amplifier, and said correction factor being substantially equal to a square root of a ratio of said ideal value of said supply current over said average value of said supply current.
 2. A power correction module for use with an amplifier driving a load impedance, said power correction module comprising: an integrator configured to generate an average value of a supply current of said amplifier in response to changes in said load impedance, said integrator utilizing a feedback voltage that is proportional to said supply current and to generate said average value of said supply current; and a correction factor block configured to receive said average value of said supply current and to provide a correction factor, said correction factor being utilized to correct a supply voltage of said amplifier.
 3. A power correction module for use with an amplifier driving a load impedance, said power correction module comprising: an integrator configured to generate an average value of a supply current of said amplifier in response to changes in said load impedance, said amplifier being utilized as a power amplifier in a transmitter system, and said transmitter system utilizing polar EDGE modulation; and a correction factor block configured to receive said average value of said supply current and to provide a correction factor, said correction factor being utilized to determine a control voltage, and said control voltage being utilized to correct a supply voltage of said amplifier.
 4. A power correction module for use with an amplifier driving a load impedance, said power correction module comprising: an integrator configured to generate an average value of a supply current of said amplifier in response to changes in said load impedance, said amplifier being utilized as a power amplifier in a transmitter system, said transmitter system including a predistortion module configured to determine a control voltage for correcting a supply voltage from a product of a corrected peak voltage and an amplitude modulation component and to output said control voltage for correcting the supply voltage of said amplifier; and a correction factor block configured to receive said average value of said supply current and to provide a correction factor represented by said corrected peak voltage, said correction factor being utilized to determine said control voltage, and said control voltage being utilized to correct said supply voltage of said amplifier.
 5. The power correction module of claim 4 wherein said transmitter system includes a phase modulator configured to receive a predistorted phase modulation component from said predistortion module and to provide a phase modulated RF input signal to said power amplifier.
 6. The power correction module of claim 4 wherein said transmitter system further includes a multiplication element configured to receive said corrected peak voltage and said amplitude modulation component and to output said product of said corrected peak voltage and said amplitude modulation component.
 7. The power correction module of claim 4 wherein the correction factor varies inversely with a square root of said average value of said supply current.
 8. The power correction module of claim 1 wherein the amplifier is configured to provide a substantially constant output power in response to the changes in said load impedance.
 9. The power correction module of claim 1 wherein the correction block is further configured to determine a corrected peak voltage, the corrected peak voltage being determined based at least partially on the correction factor.
 10. The power correction module of claim 1 wherein the amplifier is utilized as a power amplifier in a transmitter system, the transmitter system including a predistortion module configured to output a control voltage used to correct the supply voltage of the amplifier.
 11. The power correction module of claim 10 further comprising a power control/current detection circuit configured to output the supply voltage and the supply current to the amplifier in response to the control voltage and to produce a feedback voltage indicating the supply current drawn by the amplifier.
 12. The power correction module of claim 3 further comprising a multiplication element configured to receive the correction factor and a peak voltage and to output a corrected peak voltage.
 13. The power correction module of claim 2 wherein the correction factor is substantially equal to a square root of a ratio of an ideal value of said supply current over said average value of said supply current, the ideal value of said supply current being determined based at least partially on a peak voltage.
 14. The power correction module of claim 2 wherein the amplifier is utilized as a power amplifier in a transmitter system, the transmitter system including a predistortion module configured to output a control voltage used to correct the supply voltage of the amplifier.
 15. The power correction module of claim 14 further comprising a power control/current detection circuit configured to output the supply voltage and the supply current to the amplifier in response to the control voltage, said power control/current detection circuit comprising a first and a second transistor configured as a current mirror for providing a sense current, said sense current causing said feedback voltage to be substantially proportional to said supply current.
 16. The power correction module of claim 3 further comprising a look- up table configured to output an ideal value of said supply current, the correction factor block being further configured to determine the correction factor based on said ideal value of said supply current.
 17. The power correction module of claim 3 wherein the correction factor depends at least partially on a square root of an ideal value of said supply current.
 18. The power correction module of claim 3 wherein the transmitter system includes a predistortion module configured to output the control voltage.
 19. The power correction module of claim 18 further comprising a power control/current detection circuit configured to output the supply voltage and the supply current to the amplifier in response to the control voltage and to produce a feedback voltage indicating the supply current drawn by the amplifier.
 20. The power correction module of claim 19 wherein the predistortion module is configured to determine said control voltage from a product of a corrected peak voltage and an amplitude modulation component and to output said control voltage to said power control/current detection circuit. 